1. Field of the Invention
This invention relates to a backwash type particulate filter for use in an exhaust system in a diesel engine.
2. Prior Art Statement
Recently, for trucks and buses ceramic filters which remove soot contained in exhaust gas from the diesel engines are under development. These ceramic filters tend to be repeatedly used by blowing in air instantaneously into the reverse direction with respect to the exhaust gas flow and blowing away the collected soot from the filtration surfaces.
These ceramic filters are formed to have a honeycomb structure and to carry a NOx catalyst on the filtration surfaces so that their soot collecting efficiencies are high. However, when the collected soot on the filtration surfaces is burned, the temperature of the filtration surfaces rises to about 1000.degree. C. and thereby the NOx catalyst crystallizes due to the high temperature. As a result, it is rendered difficult for the catalyst to maintain its function.